Several population studies suggest that higher dietary calcium, at intake levels suggested for optimal bone health, is associated with an increased risk of aggressive prostate cancer. This may be due to reduced renal synthesis of 1,25 dihydroxyvitamin D (1,25(OH)2 D), a hormonally active form of vitamin D that acts through the nuclear vitamin D receptor (nVDR) to suppress prostate cell growth, promote differentiation, and stimulate apoptosis. Other epidemiologic studies support the hypothesis that low vitamin D stores are associated with increased prostate cancer risk. Studies in vitro show that prostate cells can convert 25-OH D into 1,25(OH)2 D. While a role for dietary modulation of vitamin D metabolite levels in prostate cancer prevention can be inferred by combining data from population and cell studies, demonstration of this phenomenon in a controlled, in vivo setting represents a significant gap in the field of prostate cancer prevention. Our hypothesis is that high vitamin D status (i.e. high serum 25-OH D) and high serum 1,25(OH)2 D protect against prostate cancer by activating genetic programs through the nVDR. We believe that dietary factors like high calcium intake will suppress the protective effect of serum 1,25(OH)2 D but not of elevated 25-OH D levels. The specific aims of the application are to: (1) Establish the relationship between dietary calcium and vitamin D intake and the protective role of serum 25-OH D and 1,25(OH)2D against prostate cancer in Wistar-Unilever rats during NMU-androgen-induced prostate carcinogenesis, (2) Establish the role of dietary calcium and vitamin D on androgen-induced proliferation and apoptosis and on protective patterns of gene expression in the prostate epithelium, and (3) Evaluate the consequence of nVDR deletion and 1alpha hydroxylase over-expression in prostate-specific IGF-1 transgenic mice predisposed to prostate carcinogenesis. In our studies we will examine stepwise carcinogenesis (PIN, carcinoma in situ, adenocarcinoma), quantitate relevant serum biomarkers, and assess expression of vitamin D sensitive proteins and genes in prostate tissue to provide insight into mechanisms whereby dietary calcium and vitamin D modulate prostate carcinogenesis through the vitamin D axis. These data will provide us with the mechanistic basis for dietary recommendations to prevent prostate cancer and optimize bone health.